Semiconductor integrated circuit

ABSTRACT

Provided is a semiconductor integrated circuit according to an exemplary aspect of the present invention including a data transmitting circuit and a data receiving circuit that receives data transmitted from the data transmitting circuit. The data transmitting circuit includes a data output circuit that outputs the data or sets an output to a high impedance state, and a control circuit that outputs a control signal to the data output circuit so that the data output circuit outputs the data when the data transmitting circuit transmits the data, and the data output circuit keeps outputting data last output in the previous data transmission, during a predetermined period after the previous data transmission when the data transmitting circuit further transmits another data after transmitting the data.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2009-206880, filed on Sep. 8, 2009, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a semiconductor integrated circuit, andmore particularly, to a semiconductor integrated circuit suitable forpower-supply noise reduction.

2. Description of Related Art

In a semiconductor integrated circuit, there has been a problem thatdata transmission between a data transmitting circuit and a datareceiving circuit is not accurately executed when power-supply noiseoccurs on signal lines used for the data transmission between thesecircuits.

Therefore, a countermeasure, for example, ODT (On Die Termination)technique has been provided to reduce the power-supply noise on signallines used for data reception of the data receiving circuit (JEDECSTANDARD, DDR2 SDRAM SPECIFICATION JESD79-2E (Revision of JESD79-2D),April 2008, JEDEC SOLID STATE TECHNOLOGY ASSOCIATION).

SUMMARY

In the related art, the countermeasure such as an ODT function has beenprovided to reduce the power-supply noise which influences the datareceiving circuit. However, the related art provides no countermeasureto reduce the power-supply noise which influences the data transmittingcircuit. Normally, the data transmitting circuit includes a data outputcircuit such as a three-state buffer for transmitting data. The datatransmitting circuit controls whether the data output circuit outputsthe data or not based on a control signal. In other words, the datatransmitting circuit controls the data output circuit to output the dataor to switch the output of the data output circuit to a high impedancestate (HiZ).

However, in the related art, the power-supply noise occurs when the datatransmitting circuit controls the output of the data output circuit tobe set to HiZ, because the supply of power supply voltage to the signallines to which the power supply voltage has continuously been suppliedis suddenly interrupted. When the data transmitting circuit switches theoutput of the data output circuit from HiZ to a data transmission stateso as to output another data before the power-supply noise converges,another data is influenced by the power-supply noise. The presentinventors have found a problem in the related art that, as describedabove, it is impossible for the data transmitting circuit to transmitthe data accurately.

An exemplary aspect of the present invention is a semiconductorintegrated circuit including:

a data transmitting circuit; and

a data receiving circuit that receives data transmitted from the datatransmitting circuit, in which

the data transmitting circuit includes:

-   -   a data output circuit that outputs the data or sets an output to        a high impedance state; and    -   a control circuit that outputs a control signal to the data        output circuit so that the data output circuit outputs the data        when the data transmitting circuit transmits the data, and the        data output circuit keeps outputting data last output in the        previous data transmission, during a predetermined period after        the previous data transmission when the data transmitting        circuit further transmits another data after transmitting the        data.

With the circuit structure as described above, it is possible totransmit data accurately by reducing the power-supply noise.

According to an exemplary aspect of the present invention, it ispossible to provide a semiconductor integrated circuit capable oftransmitting data accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary aspects, advantages and features will bemore apparent from the following description of certain exemplaryembodiments taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a semiconductor integrated circuit according to afirst exemplary embodiment of the present invention;

FIG. 2 illustrates the semiconductor integrated circuit according to thefirst exemplary embodiment of the present invention; and

FIG. 3 is a timing chart depicting an operation of the semiconductorintegrated circuit according to the first exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Specific exemplary embodiments of the present invention are described indetail below with reference to the drawings. The same components aredenoted by the same reference numerals in the drawings, and for clarityof explanation, repeated explanation is omitted as appropriate.

First Exemplary Embodiment

Referring to the drawings, a semiconductor integrated circuit accordingto a first exemplary embodiment of the present invention will bedescribed. The present invention can be applied to a circuit whichincludes a data transmitting circuit and a data receiving circuit thatreceives data transmitted from the data transmitting circuit, and whichcontrols the output of the data transmitting circuit based on a controlsignal. In this exemplary embodiment, a case is explained hereinafter inwhich the circuit shown in FIG. 1 includes an SoC (System on Chip)circuit and an SDRAM (Synchronous Dynamic Random Access Memory) circuit,and data transmission is executed between the SoC circuit and the SDRAMcircuit through a signal line for bidirectionally transmitting databetween these circuits (hereinafter, referred to simply as“bidirectional signal line”).

FIG. 1 illustrates a semiconductor integrated circuit according to thefirst exemplary embodiment of the present invention. The circuit shownin FIG. 1 includes an SoC circuit (data transmitting circuit) 100 and anSDRAM circuit (data receiving circuit) 101. Data transmission isexecuted between the SoC circuit 100 and the SDRAM circuit 101 in theDDR (double data rate) mode.

First, the circuit structure of the semiconductor integrated circuitaccording to the first exemplary embodiment of the present inventionwill be described. The SoC circuit 100 outputs a 2-bit clock signal CKand a 2-bit clock signal CKB, which is a differential signal of theclock signal CK, to the SDRAM circuit 101. The SoC circuit 100 furtheroutputs a 16-bit control signal CMD, which includes commands for eachaddress of the SDRAM circuit 101, to the SDRAM circuit 101. Note thatthe SDRAM circuit 101 receives the control signal CMD in synchronizationwith the clock signals CK and CKB.

Each of 32-bit data DQ, a 4-bit strobe signal DQS, and a 4-bit strobesignal DQSB, which is a differential signal of the strobe signal DQS, isbidirectionally transmitted and received between the SoC circuit 100 andthe SDRAM circuit 101. A receiving circuit, which is one of the SoCcircuit 100 and the SDRAM circuit 101, receives the data DQ insynchronization with the strobe signals DQS and DQSB. Note that thesignal names described above also represent the corresponding signalline names.

The circuit shown in FIG. 2 shows a 1-bit bidirectional signal line,which is one of strobe signal lines DQS[3:0] and DQSB[3:0] and a datasignal line DQ[31:0], and corresponding peripheral circuits of thecircuit shown in FIG. 1. In this exemplary embodiment, a case isexplained hereinafter in which the 1-bit bidirectional signal line isthe data signal line DQ[0]. The data signal line DQ[0] is connectedbetween the SoC circuit 100 and the SDRAM 101 as described above.

The SoC circuit 100 includes an external terminal 201, a buffer 202, adata output circuit 203 which outputs data, a termination circuit 204which has an ODT function, a control circuit 205 which outputs controlsignals to each of the data output circuit 203 and the terminationcircuit 204, and an inverter 206. The termination circuit 204 includes aresistor 207, a resistor 208, a switch 209, and a switch 210. The dataoutput circuit 203 includes a NAND circuit 251, a NOR circuit 252, atransistor 253, and a transistor 254. In this exemplary embodiment, acase is explained in which the switch 209 and the transistor 253 areP-channel MOS transistors and the switch 210 and the transistor 254 areN-channel MOS transistors.

In the SoC circuit 100, the data signal line DQ[0] is connected to aninput terminal of the buffer 202 and an output terminal of the dataoutput circuit 203 through the external terminal 201.

The termination circuit 204 is provided between the external terminal201 and the buffer 202. In the termination circuit 204, the switch 209and the resistor 207 are connected in series between a high potentialside power supply terminal VDD and a node N1 which is located on thesignal line connecting the external terminal 201 and the buffer 202. Theswitch 210 and the resistor 208 are connected in series between a lowpotential side power supply terminal VSS and the node N1. In otherwords, the source terminal of the switch 209 is connected to the highpotential side power supply terminal VDD. The drain terminal of theswitch 209 is connected to one terminal of the resistor 207. The otherterminal of the resistor 207 is connected to one terminal of theresistor 208. The other terminal of the resistor 208 is connected to thedrain terminal of the switch 210. The source terminal of the switch 210is connected to the low potential side power supply terminal VSS. Theother terminal of the resistor 207 and one terminal of the resistor 208are commonly connected to the node N1. Note that the switch 209 and theresistor 207 which are connected in series between the high potentialside power supply terminal VDD and the node N1 may be switched around.Similarly, the switch 210 and the resistor 208 which are connected inseries between the low potential side power supply terminal VSS and thenode N1 may be switched around.

An output terminal of the buffer 202 is connected to an input terminalIN used for inputting data of the control circuit 205. An outputterminal C1 of the control circuit 205 is connected to the gate terminalof the switch 209 and the gate terminal of the switch 210 through theinverter 206. Such a peripheral circuit configuration is also employedin the other bidirectional signal lines. Note that the control circuit205 is commonly provided to these bidirectional signal lines.

An output terminal OUT used for outputting data of the control circuit205 is connected to one input terminal of the NAND circuit 251 and oneinput terminal of the NOR circuit 252 in the data output circuit 203. Anoutput terminal E1 for outputting a control signal 230 of the controlcircuit 205 is connected to the other input terminal of the NAND circuit251 and the other input terminal of the NOR circuit 252 through theinverter 255 in the data output circuit 203. An output terminal of theNAND circuit 251 is connected to the gate terminal of the transistor253. An output terminal of the NOR circuit 252 is connected to the gateterminal of the transistor 254. The transistors 253 and 254 areconnected in series between the high potential side power supplyterminal VDD and the low potential side power supply terminal VSS. Inother words, the transistors 253 and 254 constitute an inverter. Thedrain terminal of the transistor 253 and the drain terminal of thetransistor 254 are commonly connected to a node which is located on thesignal line connecting between the buffer 202 and the external terminal201. Such a peripheral circuit configuration is also employed in theother bidirectional signal lines.

Next, the operation of the semiconductor integrated circuit according tothe first exemplary embodiment of the present invention will bedescribed. A case is explained hereinafter in which the SoC circuit 100receives (reads) the data such as the data DQ transmitted from the SDRAMcircuit 101. First, the SoC circuit 100 outputs the control signal CMDto the SDRAM circuit 101. After that, for example, the SDRAM circuit 101transmits the data DQ stored in a memory area of an address specified bythe control signal CMD, and the strobe signals DQS and DQSB to the SoCcircuit 100. In this case, the data DQ transmitted from the SDRAMcircuit 101 has a predetermined burst length.

The SoC circuit 100 receives each signal output from the SDRAM circuit101 through the corresponding signal line, external terminal 201, andbuffer 202. Note that the SoC circuit 100 receives the data DQ insynchronization with the strobe signals DQS and DQSB. The data DQreceived by the SoC circuit 100 is input to the control circuit 205 andthe other peripheral circuits (not shown). A period between the timewhen the SoC circuit 100 starts to transmit the control signal CMD andthe time when the SoC circuit 100 starts to receive the correspondingdata DQ is called a read latency (RL).

When receiving the data transmitted from the SDRAM circuit 101, the SoCcircuit 100 controls the ODT function of the corresponding terminationcircuit 204 to be turned on to reduce power-supply noise occurring onthe data signal line DQ and the strobe signal lines DQS and DQSB.Specifically, the SoC circuit 100 controls the switches 209 and 210,which are provided in the corresponding termination circuit 204, to beturned on based on a control signal 200 from the control circuit 205 andsets the node on the corresponding signal line to a predeterminedpotential (for example, one-half of the high potential side power supplyvoltage VDD). This makes it possible for the SoC circuit 100 to receivethe data accurately by reducing the power-supply noise included in thereceived data.

Moreover, the SoC circuit 100 controls the data output circuit 203 notto output the data to the SDRAM circuit 101 based on the control signal230 from the control circuit 205. In other words, the SoC circuit 100controls the output of the data output circuit 203 to be set to a highimpedance state (HiZ) based on the control signal 230 of L level. Theoutput of the data output circuit 203 indicates HiZ because thetransistors 253 and 254 are both controlled to be turned off when thecontrol signal 230 is L level. This makes it possible for the SoCcircuit 100 to accurately receive the data transmitted from the SDRAMcircuit 101 without being influenced by the other data output from thedata output circuit 203.

A case is explained hereinafter in which the SoC circuit 100 transmits(writes) the data to the SDRAM circuit 101. First, the SoC circuit 100outputs the control signal CMD to the SDRAM circuit 101. After that, theSoC circuit 100 transmits the data DQ and the strobe signals DQS andDQSB to the SDRAM circuit 101. In this case, the data DQ transmittedfrom the SoC circuit 100 has a predetermined burst length.

Then, the SDRAM circuit 101 receives the data DQ in synchronization withthe strobe signals DQS and DQSB. For example, the data DQ is writteninto the memory area of the address specified by the control signal CMD.A period between the time when the SoC circuit 100 starts to transmitthe control signal CMD and the time when the SoC circuit 100 starts totransmit the corresponding data DQ is called a write latency (WL).

When transmitting the data to the SDRAM circuit 101, the SoC circuit 100controls the CDT function of the corresponding termination circuit 204to be turned off. Specifically, the SoC circuit 100 controls theswitches 209 and 210, which are provided in the correspondingtermination circuit 204, to be turned off based on the control signal200 from the control circuit 205, thereby preventing the potential ofthe data transmitted to the SDRAM circuit 101 through the data outputcircuit 203 and the external terminal 201 from being decayed. This makesit possible for the SoC circuit 100 to transmit the data accurately.

The SoC circuit 100 controls the data output circuit 203 to output thedata to the SDRAM circuit 101 based on the control signal 230 from thecontrol circuit 205. In other words, the SoC circuit 100 controls thedata output circuit 203 to output the data to the SDRAM circuit 101based on the control signal 230 of H level. When the control signal 230is H level, the transistors 253 and 254 are controlled to be turned onand off in accordance with the data output from the control circuit 205.Thereby, the SoC circuit 100 transmits the data to the SDRAM circuit101.

In this manner, the SoC circuit 100 switches between a read mode inwhich the SoC circuit 100 receives the data transmitted from the SDRAMcircuit 101 and a write mode in which the SoC circuit 100 transmits thedata to the SDRAM circuit 101, based on the control signal CMD. Notethat the SoC circuit 100 outputs the control signal CMD which has a datalength corresponding to one cycle of the clock signal CK atpredetermined time intervals.

For example, the SoC circuit 100 receives data such as the data DQ inthe read mode or transmits the data in the write mode, and after thepredetermined time interval, receives or transmits another data in thesame mode. Alternatively, the SoC circuit 100 receives data such as thedata DQ in the read mode or transmits the data in the write mode, andafter the predetermined time interval, receives or transmits anotherdata in a different mode. The data transmission and reception asdescribed above is repeated.

The SoC circuit 100 according to this exemplary embodiment exhibitscharacteristics when the SoC circuit 100 transmits data such as the dataDQ in the write mode, and after the predetermined time interval,transmits another data in the write mode again. The operation of the SoCcircuit 100 in this case will be described with reference to FIG. 3.

First, the SoC circuit 100 outputs the control signal CMD (which isindicated by “A” shown in FIG. 3 and is hereinafter referred to as“write command A”) to the SDRAM circuit 101. Then, the SoC circuit 100transmits the data DQ (“D” shown in FIG. 3), which has a predeterminedburst length, and the corresponding strobe signals DQS and DQSB to theSDRAM circuit 101 after the period of the write latency WL (“C” shown inFIG. 3).

In this case, when transmitting the data, the SoC circuit 100 controlsthe corresponding data output circuit 203 to output the data.

After outputting the write command A, the SoC circuit 100 outputs awrite command E (“E” shown in FIG. 3) after the period of thepredetermined time interval (“B” shown in FIG. 3). Then, the SoC circuit100 transmits the data DQ (“G” shown in FIG. 3), which has apredetermined burst length, and the corresponding strobe signals DQS andDQSB to the SDRAM circuit 101 after the period of the write latency WL(“F” shown in FIG. 3).

In this case, the control circuit 205 calculates a period (H), in whichthe data DQ is not transmitted, based on the interval (B) of the writecommands (A, E), the write latency WL (C, F), and the burst length (D,G) of the data DQ. Based on the period thus obtained, the controlcircuit 205 determines whether the data output circuit 203 outputs thedata or not during the period (H) in which the data DQ is nottransmitted. Then, the control circuit 205 outputs the control signal230 to the data output circuit 203 based on the results of thedetermination.

When the period (H) is less than or equal to a predetermined threshold,the data output circuit 203 keeps outputting the last data (data “03”shown in FIG. 3) of the data DQ (D) during the period (H). When theperiod (H) exceeds the predetermined threshold, the data output circuit203 switches the output to HiZ during the period (H).

In the case where the write mode is repeated, when the data outputcircuit 203 keeps outputting the last data during the period (forexample, “H” shown in FIG. 3) in which the data transmission is notexecuted, power-supply noise, which may occur due to switching of theoutput to HiZ by the data output circuit 203, does not occur on thesignal line at the output side of to the data output circuit 203.Therefore, it is possible for the SoC circuit 100 to transmit the dataaccurately by reducing the power-supply noise which has been a problemin the related art.

In the case where the write mode is repeated, when the period (forexample, “H” shown in FIG. 3) in which the data transmission is notexecuted exceeds the threshold, the data output circuit 203 switches theoutput to HiZ during the period in which the data transmission is notexecuted. In this case, the power-supply noise on the correspondingsignal line caused by switching the output state of the data outputcircuit 203 converges because the period in which the data transmissionis not executed is sufficiently long. In other words, the SoC circuit100 can transmit another data output from the data output circuit 203without being influenced by the power-supply noise. This makes itpossible for the SoC circuit 100 to transmit the data accurately byreducing the effect of the power-supply noise. Note that the timing ofswitching the output of the data output circuit 203 to HiZ may bearbitrarily determined as long as the power-supply noise is converged bythe time when the next data transmission starts.

As described above, in the case where the data transmitting circuit (forexample, the SoC circuit 100) continuously transmits the data, thesemiconductor integrated circuit according to this exemplary embodimentcontrols the output of the data output circuit (for example, the dataoutput circuit 203) included in the data transmitting circuit based on adata transmission interval. In other words, the semiconductor integratedcircuit according to this exemplary embodiment controls the data outputcircuit continuously to output the data or to switch the output to HiZ.This makes it possible for the semiconductor integrated circuitaccording to this exemplary embodiment to transmit the data accuratelyby reducing the effect of the power-supply noise.

Note that the present invention is not limited to the above exemplaryembodiments, but can be modified as appropriate within the scope of thepresent invention. For example, though the above-mentioned exemplaryembodiments have described an example in which the SoC circuit 100transmits the data to the SDRAM circuit 101, the present invention isnot limited thereto. The present invention is also applicable to acircuit configuration in which the SDRAM circuit 101 transmits the datato the SoC circuit 100. In this case, the data output circuit includedin the SDRAM circuit 101 must be controlled as in the case of the dataoutput circuit 203 included in the SoC circuit 100.

Though the above-mentioned exemplary embodiments have described anexample in which, when the data transmitting circuit (for example, theSoC circuit 100) continuously transmits data, the control circuit 205outputs the control signal (for example, the control signal 230) basedon the interval of the address command such as a write command, thewrite latency WL, and the burst length of the data DQ, the presentinvention is not limited thereto. The present invention is alsoapplicable to a circuit configuration for outputting the control signal(for example, the control signal 230) based on at least one of theabove-mentioned pieces of information (for example, the interval of theaddress command) if it is possible to control the output of the dataoutput circuit 203 based on the data transmission interval.

Though the above-mentioned exemplary embodiments have described the casewhere the signal line which is used for the output of the data outputcircuit 203 is a bidirectional signal line, the present invention is notlimited thereto. The present invention is also applicable to a circuitconfiguration in which the signal line which is used for the output ofthe data output circuit 203 is a signal line dedicated for transmittingdata.

The termination circuit is not limited to the circuits illustrated inthe above-mentioned exemplary embodiments. The present invention is alsoapplicable to a circuit configuration including a resistor and a switchwhich are connected in series between the power supply terminal havingthe predetermined potential (for example, one-half of the high potentialside power supply voltage VDD) and the node on the corresponding signalline. Moreover, though the above-mentioned exemplary embodiments havedescribed the case where the termination circuit is included, thepresent invention is not limited thereto. The present invention is alsoapplicable to a circuit configuration in which the termination circuitis not included.

Though the above-mentioned exemplary embodiments have described anexample in which the semiconductor integrated circuit includes a singleSDRAM circuit, the present invention is not limited thereto. Thesemiconductor integrated circuit according to the present invention isalso applicable to a circuit configuration including a plurality ofSDRAM circuits.

While the invention has been described in terms of several exemplaryembodiments, those skilled in the art will recognize that the inventioncan be practiced with various modifications within the spirit and scopeof the appended claims and the invention is not limited to the examplesdescribed above.

Further, the scope of the claims is not limited by the exemplaryembodiments described above.

Furthermore, it is noted that, Applicant's intent is to encompassequivalents of all claim elements, even if amended later duringprosecution.

1. A semiconductor integrated circuit comprising: a data transmittingcircuit; and a data receiving circuit that receives data transmittedfrom the data transmitting circuit, wherein the data transmittingcircuit comprises: a data output circuit that outputs the data or setsan output to a high impedance state; and a control circuit that outputsa control signal to the data output circuit so that the data outputcircuit outputs the data when the data transmitting circuit transmitsthe data, and the data output circuit keeps outputting data last outputin the previous data transmission, during a predetermined period afterthe previous data transmission when the data transmitting circuitfurther transmits another data after transmitting the data.
 2. Thesemiconductor integrated circuit according to claim 1, wherein thepredetermined period is decided based on a data transmission interval ofthe data transmitting circuit.
 3. The semiconductor integrated circuitaccording to claim 2, wherein the data transmission interval is decidedbased on a period between a time when the data transmitting circuitoutputs a command for transmitting data to the data receiving circuitand a time when the data transmitting circuit further outputs a commandfor transmitting another data to the data receiving circuit.
 4. Thesemiconductor integrated circuit according to claim 2, wherein the datatransmission interval is decided based on a latency between a time whenthe data transmitting circuit outputs a command for transmitting data tothe data receiving circuit and a time when the data transmitting circuitstarts to transmit the data.
 5. The semiconductor integrated circuitaccording to claim 2, wherein the data transmission interval is decidedbased on a burst length of the data.
 6. The semiconductor integratedcircuit according to claim 2, wherein the control circuit outputs thecontrol signal so that the output of the data output circuit is set tothe high impedance state instead of keeping outputting data last outputin the previous data transmission when the data transmission circuitfurther transmits another data after transmitting the data and when thedata transmission interval exceeds a predetermined threshold.
 7. Thesemiconductor integrated circuit according to claim 1, wherein the dataoutput circuit comprises an inverter that includes a P-channel MOStransistor and an N-channel MOS transistor, and the P-channel MOStransistor and the N-channel MOS transistor are turned off when theoutput of the data output circuit is set to the high impedance state,and one of the P-channel MOS transistor and the N-channel MOS transistoris turned on and the other is turned off based on the data when the dataoutput circuit outputs the data.